SHARKS IN PERIL: THREATS and OVERFISHING – PART 2

Fish reproductive rates vary, affecting their sustainability to fishing. Species such as sharks and rays, which reproduce slowly, are particularly susceptible to overfishing. If we deplete shark populations faster than they can reproduce, we face dwindling numbers and reduced future catches. 

Threats 

While sharks reign as apex predators in ocean ecosystems, humans exploit them for various purposes, from shark leather belts and teeth souvenirs to practices like accidental bycatch in commercial fishing or finning for soup. Consequently, many species face endangerment, contributing to a dramatic decline in their population. Major threats include:

  1. Shark fin soup: This dish became popular in the 1900s and has led to an estimated 86+ million sharks killed globally per year as of 2023. Shark fin soup production involves catching sharks, removing their fins, and discarding them back into the ocean to suffer prolonged and agonizing deaths.
  2. Nutritional supplements: Endangered deep-sea shark species are targeted for shark liver oil, marketed to consumers with false claims of health benefits. Similarly, shark cartilage pills are promoted as having anti-cancer properties, despite them being vulnerable to cancer themselves. 
  3. Commercial fishing: Sharks, along with turtles, dolphins, and other marine creatures frequently fall victim to fishing nets. Overfishing not only reduces the prey of ocean predators but also results in the accidental capture and death of numerous non-target species. 
  4. Recreational fishing: Sharks are pursued and slaughtered for recreational purposes, with their teeth, skin, and cartilage often preserved as trophies or sold as trinkets and souvenirs.
  5. Culling: Environmental changes are bringing sharks closer to human habitats, increasing interactions. Additionally, fishermen sometimes lure sharks to coastal areas using dolphins as bait. While shark encounters are relatively rare, only 10 percent result in fatalities.
  6. Sensationalistic media coverage: Exaggerated narratives portray sharks as aggressive predators that purposefully target humans, fueling unawareness about their crucial role in ocean ecosystems. Some have even been swayed to advocate for the removal of the protected status of great whites and support shark culling initiatives.

Killer whales

Since 2009, there has been a rise in killer whale sightings in False Bay, South Africa. This area is known to be home to the sevengill shark, with scuba divers seeing as many as 70 in a single dive. But, in 2015, they noticed something odd: overnight the sharks seemed to disappear. Shortly after, carcasses of several sevengills washed up on the seabed. 

In April 2016, five more sevengills washed up on shore with pectoral tears and missing livers. Astoundingly, the tears photographed in 2015 were a perfect match with one characteristic: orca tooth impressions. Then in 2017, five great whites washed up on shore in Gansbaai, also without their livers. 

The culprits? Two orcas, known as ‘Port’ and ‘Starboard.’ But why are they targeting sharks? Some experts think that Port and Starboard belong to a subgroup, or “ecotype” of orcas commonly found in the ocean. However, they may have moved closer to shore in response to fishing activities reducing their usual prey.

Another theory suggests that they, either individual or within their subgroup, have adopted a novel behavior to preserve their teeth. When orcas bite into the rough skin of sharks, their teeth can wear down. The nutritional liver of great whites is filled with rich oily fat and offers a complete meal without the effort of potential tooth damage involved in tearing sharks apart.

Regardless of whether Port and Starboard are the trailblazers of this shark-eating behavior, it’s likely it will continue. 

Overfishing

Healthy shark populations are vital for maintaining a balanced ocean ecosystem. As apex predators, they regulate food webs and prevent instability. Overfishing of sharks can disrupt these ecosystems, leading to potential collapse. Recent research highlights their role in controlling the behavior of other species, such as tiger sharks preventing overgrazing of seagrass by turtles and dugongs. This indirect regulation helps maintain the health of seagrass habitats, which serve as nurseries for small fish and store carbon for thousands of years at a rate much faster than terrestrial forests.

Sharks are known for their long lifespan and slow maturation, typically reaching maturity around 10 years, and giving birth to only giving birth to only 2-12 pups ever 1-2 years. This reproductive pattern makes them highly susceptible to overfishing, leading to a drastic 70 percent decline in their populations within the past 50 years.

In the past century of industrialized fishing, overfishing has led to the extinction of a third of shark and ray species. To put this into perspective, sharks have thrived for approximately 450 million years, enduring four of the five mass extinctions. Yet, the impact of overfishing has caused significant damage in just a fraction of that time, approximately 0.02 seconds on a 24-hour clock of their existence.

Environmental impact of overfishing sharks

The overfishing of dusky sharks (Charcharhinus obscurus) in Western Australia’s Northern Shark Fishery (NSF) in the early 2000s caused a notable decline in their juvenile population over 1000km away. Predominantly mature adults in the NSF region make a return-trip to the temperate south of Western Australia, spanning over ~1000-4000 km, where they give birth. However, overfishing in the north reduced the number of juveniles in the south, causing concern among local fishers. Luckily, since the closure of the NSF in 2010 to address overfishing, sandbar populations are slowly recovering, and dusky numbers are stabilizing.

In South Africa, overfishing is believed to be disrupting the food web, with school and smooth-hound sharks being heavily targeted. This, combined with increased predation by orcas, is driving away white sharks for extended periods. Consequently, the absence of white sharks has led to an increase in bronze whalers and sevengill sharks, while seals, feeling less threatened, are reproducing more and hunting extensively. These cascading effects highlight the potential collapse of ecosystems due to shark overfishing.

How to stop overfishing

The cornerstone of any sustainable fishery lies in the independent observation of fishing activities, whether through human observers or onboard cameras. This data collection allows us to understand species composition, catch locations, and quantities accurately. While achieving 100 percent coverage may not always be feasible, scientifically determined observation levels provide a strong representation of fishing activity over time and space.

For threatened shark species facing overfishing, detailed data from independent observation and fishers’ logbooks enable the establishment of mortality limits. Once these limits are reached, fishing activities can be appropriately slowed or halted to facilitate species recovery. Certain species—termed ‘choke’ species—can trigger fishery closures when their mortality limits are met.

Protecting critical habitats, such as aggregation sites and breeding grounds, is vital for promoting the recovery of threatened species by minimizing interactions with fisheries and allowing populations to increase over time. 

Are sharks man-eaters? 

Sharks may be considered the most-feared animal on Earth, especially due to the 1975 release of Jaws. Although attitudes may be changing, humans have historically focused more on the exaggerated threat posed by sharks rather than recognizing their key role in marine ecosystems. 

Considering the significant number of people using the ocean near sharks, it’s evident that shark attacks on humans are rare, and fatal incidents are even rarer. Scientists have been advocating for not using the term “shark attack” when referring to most shark-human encounters and instead using “shark encounter” or “shark bite” for the majority of instances. 

For example, in Florida, where most unprovoked shark encounters occur globally, injuries are typically minor, often involving small sharks like blacktips. These incidents usually include single nips or chomps, as the sharks mistake a swimmer’s hand or foot for their usual prey in murky nearshore waters. 

But ask yourself this: if a shark bites a surf or paddleboard without coming in contact with the person on top, and then swims off (which is usually the case), is that really considered an attack?

While it’s impossible to determine how many humans have been eaten by sharks, there are different factors that complicate making an accurate assessment of the phenomenon. Even today, shark attacks go unreported but are being blamed for why a person goes missing at sea, even if nobody was there to witness it. 

In some rare instances of fatal shark attacks that are officially confirmed, only part of the victim’s body is recovered, like the 2014 attack on spear fisher Sam Kellett in South Australia or the 2022 incident involving a snorkeler off Maui’s Keawakapu Beach, where no remains were found. It remains uncertain whether the attacking shark consumed all or part of the victim, as body parts could sink to the ocean floor or be eaten by other animals.

You’re probably wondering why and how sharks bite people. Research and speculation have focused on the motives behind shark attacks and bites, especially concerning the ‘Big Three’ (bull, tiger, and great white). Predatory attacks, where sharks initially perceive humans as potential prey, may lead to partial or complete consumption of the victim’s body. Other possible reasons for shark bites include defensive reactions to feeling threatened or territorial responses, as seen in some attacks on boats.

It’s reassuring to note that shark attacks on humans are exceedingly rare, considering you have a greater chance of being struck by lightning. By adhering to common-sense precautions like avoiding swimming at night or dusk, the already low risk of encountering a shark is further reduced. If an encounter does occur, it’s more probable to result in minor bites rather than a serious predatory attack.

FIN-ishing Thoughts

  • Overfishing and human exploitation are significant threats to sharks. 
  • Sharks AREN’T man-eaters. 
  • Human observation, onboard cameras, and fisher logbooks can help prevent overfishing of sharks.

Get ready for the gripping conclusion: “Sharks at Risk: Habitat Destruction and Conservation Status.” Discover the harrowing tale of how shark habitats are vanishing, explore the precarious conservation status of these majestic creatures, and uncover the heroic efforts being made to save them.